Drug-Ion Exchanger Interactions: Description by the langmuir adsorption isotherm

In pharmaceutics, the principle of ion exchange can be used in drug delivery systems, among others as depot formulations. However, in pharmaceutical preparations on the market, their use is limited, possibly due to difficulties in the prediction of release properties of such formulations. To make such prediction possible, first, the binding process of drug substance to the ion exchange material need to be investigated. Beside calorimetric measurements, which determine the strength of the binding between the components, investigations of adsorption processes are of crucial importance for the understanding of the interactions involved in ion exchange processes. The Langmuir adsorption approach seems to be suitable for the description of ion exchange systems in technical fields. However, particularly in those systems used for technical purposes, the amount of ion exchange material exceeds the amount of exchangeable ion to a huge extend. In the development of depot formulations on the other hand, the aim is to bind as much drug substance as possible to the / "carrier" / ion exchanger. The relation in amount of the two components is therfore quite different in comparison to other systems. The purpose of the present study is to discuss the possibilities and limitatons of the langmuir adsorption approach with respect to the ion exchange system Amberlite IRP 69 / propranolol hydrochloride.